aws-lambda-dotnet

packaged by Chainguard

Chainguard Container for aws-lambda-dotnet

AWS provided base images for Lambda contain all the required components to run your functions packaged as container images on AWS Lambda.

Chainguard Containers are regularly-updated, secure-by-default container images.

Download this Container Image

For those with access, this container image is available on cgr.dev:

docker pull cgr.dev/ORGANIZATION/aws-lambda-dotnet:latest

Be sure to replace the ORGANIZATION placeholder with the name used for your organization's private repository within the Chainguard Registry.

Compatibility Notes

Chainguard's aws-lambda-dotnet container image is a drop-in replacement for the upstream public.ecr.aws/lambda/dotnet image, with improved security and few-to-zero CVEs. Switching to this image should not require any changes to your existing deployment configuration.

The tag scheme differs from upstream, though both publish rolling major tags (8, 9, 10) and latest, so a FROM line pinned to a major behaves the same:

• Immutable pins. Upstream pins a build by date, such as 10.2026.08.16.14. This image pins the .NET runtime version instead — 10.0.11, with 10.0 as an intermediate stem — because that is the version the image reports in DOTNET_VERSION, and it says what changed rather than when it was built. There is no date-stamped equivalent; pin the digest for a byte-exact reference.
• Architectures. Upstream publishes per-architecture tags such as 10-x86_64 and 10-arm64. Every tag here is a multi-architecture manifest covering both x86_64 and aarch64, so no suffix is needed and the container runtime selects the right image.
• Development variants. Each tag has a -dev counterpart, such as 10-dev, adding a shell, a package manager, and the matching .NET SDK; upstream has no equivalent. Tags are also published with a v prefix (v10, v10.0.11) as aliases.

One difference is worth knowing: this image ships no rpm, dnf, or microdnf, so a Dockerfile that installs native OS dependencies on top of the base image will not work as written. Install them in the -dev variant, which includes a shell and package manager, and copy the result into the production image with a multi-stage build, as shown in Getting Started.

This image runs as root, matching upstream, which sets no USER. AWS Lambda overrides the user at execution time, so this mainly affects local testing.

Prerequisites

• A container runtime such as Docker.
• A .NET project targeting the same major version as the tag you select. The -dev variant carries the matching .NET SDK, so a local SDK installation is not required when you build inside the image.

Getting Started

A .NET Lambda function is a compiled assembly, so it must be published before it can run. Build it in the -dev variant and copy the publish output into /var/task, which keeps the build and runtime .NET versions aligned:

cat > Dockerfile <<'EOF'
FROM cgr.dev/ORGANIZATION/aws-lambda-dotnet:latest-dev AS build
WORKDIR /src
COPY . .
RUN dotnet publish -c Release -o /publish

FROM cgr.dev/ORGANIZATION/aws-lambda-dotnet:latest
COPY --from=build /publish ${LAMBDA_TASK_ROOT}
CMD ["MyFunction::MyFunction.Function::FunctionHandler"]
EOF

Build and start the function:

docker build -t my-function .
docker run --rm -p 8080:8080 my-function

The CMD is the handler reference. For a class library handler it takes the form ASSEMBLY::NAMESPACE.CLASS::METHOD; for an executable assembly handler, which bootstraps the runtime itself through LambdaBootstrapBuilder, it is just the assembly name.

When AWS_LAMBDA_RUNTIME_API is unset, as in the example above, the container runs under aws-lambda-rie and exposes the local Lambda invocation API on port 8080:

curl -XPOST "http://localhost:8080/2015-03-31/functions/function/invocations" \
  -d '{"hello":"world"}'

Configuration

bootstrap locates your function by looking for <assembly>.deps.json and <assembly>.runtimeconfig.json in /var/task. When it cannot derive the assembly name from the handler, it falls back to globbing, and resolution fails if /var/task contains more than one candidate of either file. Naming the entry assembly explicitly avoids that ambiguity and skips the glob, which also trims a small amount of cold-start time:

ENV LAMBDA_DOTNET_MAIN_ASSEMBLY=MyFunction

This is worth setting whenever your publish output includes several assemblies with their own deps.json, such as a function that ships plugins alongside the handler.

Documentation and Resources

• Deploy .NET Lambda functions with container images
• Define Lambda function handler in C#
• AWS Lambda Runtime Interface Emulator
• Chainguard Academy

What are Chainguard Containers?

Chainguard's free tier of Starter container images are built with Wolfi, our minimal Linux undistro.

All other Chainguard Containers are built with Chainguard OS, Chainguard's minimal Linux operating system designed to produce container images that meet the requirements of a more secure software supply chain.

The main features of Chainguard Containers include:

• Minimal design, without unnecessary software bloat
• Daily builds to ensure container images are up-to-date with available security patches
• High quality build-time SBOMs attesting to the provenance of all artifacts within the image
• Verifiable signatures provided by Sigstore
• Reproducible builds with Cosign and apko (read more about reproducibility)

For cases where you need container images with shells and package managers to build or debug, most Chainguard Containers come paired with a development, or -dev, variant.

In all other cases, including Chainguard Containers tagged as :latest or with a specific version number, the container images include only an open-source application and its runtime dependencies. These minimal container images typically do not contain a shell or package manager.

Although the -dev container image variants have similar security features as their more minimal versions, they include additional software that is typically not necessary in production environments. We recommend using multi-stage builds to copy artifacts from the -dev variant into a more minimal production image.

Need additional packages?

To improve security, Chainguard Containers include only essential dependencies. Need more packages? Chainguard customers can use Custom Assembly to add packages, either through the Console, chainctl, or API.

To use Custom Assembly in the Chainguard Console: navigate to the image you'd like to customize in your Organization's list of images, and click on the Customize image button at the top of the page.

Learn More

Refer to our Chainguard Containers documentation on Chainguard Academy. Chainguard also offers VMs and Libraries — contact us for access.

Trademarks

This software listing is packaged by Chainguard. The trademarks set forth in this offering are owned by their respective companies, and use of them does not imply any affiliation, sponsorship, or endorsement by such companies.